1. Field of the Invention
The present invention relates to an illumination system, and more particularly, to an illumination system for a projector.
2. Descriptions of the Related Art
Solid state light sources such as light emitting diodes (LEDs) or lasers have a long service life, a small volume and mercury-free. However, when being used as light sources for projectors, solid state light sources are still inferior to conventional high-pressure mercury lamps in terms of the luminance they provide. Therefore, although the solid state light sources are used more widely, they have not yet completely replaced the conventional high-pressure mercury lamps in the field of projection apparatuses.
On the other hand, to enable a light source in a projector to uniformly project light of the three primary colors (red, blue and green) to facilitate the coupling operation performed by a light coupling assembly disposed in the projector, the following two approaches are mostly used in the prior art to output the light of the three primary colors (red, blue and green). The first approach is to use a solid state light source to project a white light, and then enable the white light to pass through a color wheel with red, blue and green colors to generate the corresponding red, blue and green timing light, respectively for light coupling and output. The second approach is to use the blue laser as a solid state light source to excite phosphor powders coated on the rotary disk to generate a red, blue, green or yellow light, and then couple the blue light emitted by the blue laser with the red, green or yellow light for output, thereby obtaining the desired image.
In detail, an illumination system using the blue laser as the solid state light source in the second approach is as shown in FIG. 8. The illumination system 800 in a projector of the prior art comprises a blue laser light source 810, a red LED light source 820, a first color separating mirror 830, a second color separating mirror 840, a mirror wheel 850, two reflecting mirrors 860 and a light homogenizing component 870. A specific area of the mirror wheel 850 is coated with a green phosphor, and an uncoated portion thereof is a transmitting area.
When blue light 801 of the blue laser light source 810 passes through the first color separating mirror 830 to the specific area of the mirror wheel 850, the green phosphor is excited to generate a green light 802, which is then reflected by the first color separating mirror 830 to the light homogenizing component 870; when the blue light 801 is projected to the transmitting area of the mirror wheel 850 and is transmitted therethrough, the blue light 801 is reflected by the reflecting mirrors 860 behind the transmitting area and by the second color separating mirror 840 to the light homogenizing component 870. On the other hand, a red light 803 provided by the red LED light source 820 passes through the first color separating mirror 830 and the second color separating mirror 840 to the light homogenizing component 870.
However, although the aforesaid two approaches can use the light beams emitted by the solid state light sources to form the red, blue and green light (and optionally, a yellow light) for light coupling purposes, both the aforesaid approaches result in divergent light and suffer from low efficiency due to limitations of inherent optical properties of the light sources. In particular for the second approach, the blue light for exciting the green phosphor cannot be fully converted into the green light and the blue light must be recycled by the reflecting mirrors from behind, which makes the optical path of the blue light elongated; consequently, this light coupling approach fails to provide an effective solution in terms of the blue light and the green light that is generated through excitation.
Therefore, the light coupling approaches of the prior art not only provide a limited effect in improving the efficiency of generating the green light, but also increase the volume, weight and manufacturing cost of the overall system due to the use of reflecting mirrors, which makes the related products uncompetitive in the market.
Accordingly, an urgent need exists in the art to increase the utilization efficiency of the light sources.